The release of chemical or biological agents over a large urban area would be devastating. The amount of contaminated homes, buildings, furniture, automobiles and all the materials within them that could never completely be decontaminated would generate a disposal waste load similar to a tornado ripping through the middle of a town, except that handling it could be life threatening. The worst items would probably be decontaminated in place, but tons of low level contaminated waste would have to be handled and transported to waste landfills, incinerators or other treatment facilities. The effort required to prevent further spread of the contamination during the transport of this contaminated material would be labor intensive and very costly; the EPA calculates that the cost of moving this contaminated waste could be several billion dollars (Lemieux, P., 2011. BOTE Preliminary Results: Cost Analysis. Durham, N.C., U.S. EPA Decontamination Research and Development Conference). A method to safely encapsulate the contaminated waste materials, thus preventing the spread of contamination and simplifying its handling and disposal, would speed up the recovery effort and significantly decrease the overall cost of the remediation. There is a need for a hazardous waste cleanup method that simplifies both the transport and disposal of materials that must be removed.
Solid waste encapsulation is known for immobilizing radioactive materials and toxic metals (lead, mercury); the reported process uses Portland cement. This encasement is not appropriate for solids contaminated with chemical or biological threats, because it adds excessive mass and eliminates combustion as the ultimate disposal method. Solid waste encapsulation for chemical or biological hazards must use materials and application methods to provide a barrier that encapsulates the chemical and biological contaminated materials, producing a solid waste that is not hazardous to transport and may be disposed of by less expensive methods than hazardous waste landfills. It is desirable to use the minimum weight and volume of material to simplify logistics and lower the application and transport cost, while producing a barrier that resists damage by handling during transport.
U.S. Pat. No. 5,276,255A, “Cementitious encapsulation of waste materials and/or contaminated soils containing heavy metals, to render them immobile” teaches a method of cementitious encapsulation of waste materials and/or contaminated soils containing heavy metals, to render them immobile, and particularly to the immobilization of metals, in regulated amounts, in such wastes.
Encapsulation processes to stabilize wastes for storage, transport or disposal include the use of Portland cement or related inorganic materials (Sharp, J., Milestone, N., Hill, J. & Miller, E., 2003. Cementitios Systems for encapsulation of intermediate level waste. Oxford, England, International conference on radioactie wast menagement and environmental remediation). This approach has been applied to radioactive wastes and those containing toxic metals such as mercury (Kalb, P., Heiser III, J. & Colombo, P., 1991. Modified sulfur cement encapsulation of mixed waste contaminanted incinerator fly ash. Waste Management, 11(3), pp. 147-153). In such cases this is a solution, because the contaminant cannot be detoxified by chemical means and must be stabilized for permanent storage. However, in the case of chemical or biological agents, the criteria are quite different. In this case the requirements are that contaminated waste be stabilized for interim storage and transport with minimal cost and weight (to lower the cost of transport), with simplified logistics, and preferably using combustible encapsulation materials so that the wastes can be incinerated after transport to a suitable incinerator or gasifier.
In a large-scale chemical or biological event it will be essential to transport a high volume of material that may be contaminated, but for which it would be too time-consuming and expensive to sample or decontaminate every item or batch. That consideration demands an effective barrier, which must be easy to apply and be capable of fitting on various shaped materials. Liquid polyethylene macroencapsulation is another hazardous waste encapsulation method, but it suffers from the limitation that it must be applied hot (as a polymer melt).
U.S. Pat. No. 5,962,630A “Process and material that encapsulates solid hazardous waste” teaches a method using a thermoplastic polymer and sulfur to encapsulate waste. A method (I) for encapsulating mixed waste comprises mixing a thermoplastic polymer (i) having a melting point temperature of less than 150° C., elemental sulfur (ii) and mixed waste (iii), at an elevated temperature of no greater than 200° C. The mixture is intimately mixed and then cooled to form a solid. An independent claim is also included for a composition of matter (II) comprising (i), (ii) and (iii). (i) is present at 2-10% by weight of (ii), and (iii) is present at up to 40% by weight.
U.S. Pat. No. 7,250,119B2 “Selective polymer wrapping of radioactive materials” teaches the encapsulation of radioactive particles and/or other materials partially or completely involves exposing radioactive particles or materials, to a precursor monomer solution. The monomer solution polymerizes in situ by the inherent radiation irradiated from the radioactive material, whereby partially or totally encapsulating the radioactive particles with the resulting polymer.
Polyethylene (PE) has previously been used to stabilize mixed wastes, in processes that add the PE at temperatures where it is liquid (typically above 250° F.). Example processes include microencapsulation, in which the waste is combined with molten plastic in an extruder to form a homogeneous mixture, which cools to a monolithic solid (Polyethylene Macroencapsulation: mixed waste focus area. U.S. Department of Energy, February 1998, by Brookhaven National Lab), and is incorporated by reference herein. A more recent development, suited to larger particle sizes, is termed macroencapsulation, and can be accomplished by liquefying the PE in an extruder and adding the liquid polymer to the waste in a suitable container. Again, cooling yields a solid. Polymer macroencapsulation is effective for radioactive lead solids and mixed waste debris, defined as “materials exceeding 60 mm in particle size.” Under current regulations, lead-containing waste that is macroencapsulated through this process does not require performance testing such as EPA's Toxicity Characteristic Leaching Procedure (TCLP) (Brookhaven National Laboratory, 2009). This example demonstrates that appropriate macroencapsulation can transform a regulated waste into a material that is suitable for landfill disposal, and in some cases does not even require TCLP characterization for landfill disposal.
Due to the high cost of obtaining permits to transport hazardous wastes, costly alternatives have been investigated, including portable incinerators for on-site destruction. However, portable incinerators may not be allowed in sensitive locations, such as near populated urban areas or national monuments. In addition, testing of spore kill within a portable incinerator has shown that spores survive longer than expected; in some cases EPA tests showed only a 3-log reduction in viable spores. Therefore, portable incinerators may not offer the level of control required to ensure proper kill of bacterial spores (Dun, S. & Wood, J., 2009. Report on the 2008 Workshop on Decontamination Research and Associated Issues for Sites Contaminated with Chemical, Biological, or Radiological Materials, EPA/600/R-09/035). There was concern that the exhaust plume might actually spread the contamination. In addition these portable devices would only be capable of handling smaller materials such as protective clothing, not building materials. For the larger contaminated materials, ways and means to safely contain the wastes at low cost so they can be transported to large scale treatment facilities are required.
All of these references contain at least one of the following shortcomings: The method adds too much weight, the method cannot be used to encapsulate the waste object on site, the encapsulation cannot be applied at the ambient temperature of the contamination site, or the encapsulated objects cannot be incinerated because the encapsulating material cannot be incinerated.
Thus, there is a significant need in the art for a method to encapsulate and stabilize materials for safe interim on-site storage and transport to a disposal site that does not add excessive weight, that does not limit disposal options, that is an effective barrier to contain the hazard, that can be applied on-site at or near the ambient temperature, and that can lower the cost of remediating a hazard site.